Variable speed cantilevered shaft pumps



Dec. 29, 1964 w. D. HAENTJENs VARIABLE SPEED CANTILEVERED SHAFT PUMPS Filed Jan. 4, 1963 INVE'TR. WALTER D. HAENTJENS ATTYVS.

United States Patent Office lhli? Patented Dec. 29, 1964 3,163,117 VARIABLE SPEED CANTILEVERED SHAFT PUMPS Walter D. Haenttens, RJ). l, Sugarloaf, Pa. Filed Jan. 4, 1963, Ser. No. 24,455 7 Claims. (Cl. 103--87) This invention relates to cantilevered shaft pumps for use in laboratories, pilot plants, and other situations where water, liquids, or slurries of any type must be moved from a sump or other space and where exact operating conditions cannot be determined in advance, and more particularly to a variable speed pump characterized by no severe vibration in a vertically cantilevered pump shaft that supports a pump impeller a distance below the pump drive assembly.

Heretofore, it has been known that cantilevered shaft pumps have inherent critical speeds at which high vibration, lost pressure, and low eiciency are obtained, not to mention increased pump wear and possible breakage of the pump or its components. In fact, it is almost impossible to operate a cantilevered pump at or near the critical speed of the pump.

The critical speed of such pumps is equal to the resonant frequency of the cantilevered pump shaft, which frequency is a function of the shaft length and mass, and of the impeller mass, and also, to some degree, of the type of shaft support. Therefore, to change the resonant frequency of a pump and thus the critical speed, it is necessary to change one or more of the factors previously mentioned (i.e. shaft lengt shaft mass, impeller mass, or supporting structure).

It is the general object of the invention to overcome and avoid the foregoing and other difficulties of and objections to prior art practices by the provision of a cantilevered shaft pump, wherein the speed can be varied to any r.p.m. without changing the constructed shaft length or its permanent mass, or the impeller mass, or the shaft supporting structure of the pump. A

Another object of the invention is to provide a cantilevered shaft pump wherein the critical speed of the pump can be varied very easily by adding a small, ciroumferentially distributed, weight to the shaft to change the mass of the shaft, or by moving a weight vertically on the shaft to change the vertical mass distribution of the shaft.

Another object of the invention is to provide a cantilevered shaft pump wherein the rotational speed of the pump can be varied to any speed desired and still lnot approachy a critical speed, and the aforesaid being accomplished by changing the amount, or the position of a weight circumferentially positioned on and secured to the cantilevered shaft.

For a'better understanding of :the invention, reference should be had to Vthe accompanying drawings, wherein:

FIG. 1 is a front vertical cross sectional View of a pump comprising one embodiment of the invention; and

FIG. 2 is a horizontal cross sectional View of the pump shaft taken on line 24-2 of FIG. l.

This invention is an improvement upon the type of pumps disclosed in my earlier United States Letters Patents Nos. 2,625,110 and 2,890,659, and in my newly issued Patent No. 3,066,612, dated December 4, 1.962.

Generally speaking, the invention relates tothe combination of a load carrying rotatably mounted, vertically cantilevered shaft which is of essentially the same diamel ter throughout its length, with a weight means on the shaft, and screw means securing the weight means removably to the shaft at any portion thereof, which weight circumferentially surrounds and is at least substantially equally circumferentially distributed on the shaft so that the rotating mass distribution of the shaft is changed by the weight when moved axially thereof.

With specic reference to the form of the invention illustrated in the drawings, the numeral l@ indicates generally a cantilevered shaft pump including a motor 12 on top, a pump assembly 14 on the bottom, and a shaft 16 extending between the pump assembly 14 and the motor 12.

The pump assembly 14 is supported by a pair of discharge pipes or tubes l and 20, and with the pump assembly 14 being of the twin discharge type adapted for pumping liquids upwardly vertically through the discharge tubes 18 and 20. These tubes connect to a common outlet head 22 provided on an upper housing portion of the apparatus.

The pump assembly 14 of the invention comprises a top, or bottom inlet pump casing, or housing 24 that has an inlet 26 therein, an upper plate 2S, and a lower plate 30. An impeller 32 for the pump is positioned within the casing 24 by the shaft f6, and held in place by means of a nut 44. A pump impeller 32 smoothly seats in and seals the inlet 26 so that all liquids passing into the casing must ow through the impeller 32. Suitable centrifugal pumping vanes 34 are provided at radially spaced portions of the impeller 32 for forcing liquid through the pump casing 24 and out of the casing 24, up to and through a discharge head 25 that connects to the dis charge tubes 18 and 20 for dow from the apparatus. For a more detailed description of the pump assembly, reference should be had to my earlier United States Letters Patent No. 2,625,110 entitled Pump for Vertical Movement of Liquids. f

The shaft i6, aliixed to the motor l2 by means of a suitable coupling 38, rides in ball bearings 4i) and 42, while means such as a slinger ring 46 are provided to keep liquid, or solids from passing up the shaft 16 to the area of the ball bearings d0 and 42. That portion of the shaft below the slinger ring 46 and above the pump assembly 14 is turned to the same circumference.

As an important feature of the invention, a circularly shaped weight 48 is movably mounted on the shaft i6. With specific reference to FiG. 2, it can be seen that the weight i8 is split vertically into two equal halves Si? and 52. The two halves 50 and 52 are removably held together, as by screw means 54. The weight 43 is positioned on the shaft lo by any suitable'means, such as a set screw 56 bearing on the shaft surface. Therefore, it

' can be seen that the weight 4S can be removed from the shaft by removing screws 54, or since the shaft i6 is of the same diameter throughout its length between the slinger ring 46 and the pump assembly 14, the weight 4d can be positioned at any desired vertical point on the shaft 16 between these limits, by means of the set screw 56.

Again, it is noted that this type of cantilevered shaft pump is quite sensitive to rotational operation in close proximity to the critical speed. The critical speed of such shafts is equal to the resonant frequency which is a function of theV shaft length and mass, and the impeller mass and also to some degree, the type of shaft support and the total mass distribution. Therefore, by simply moving the weight 4S up or down on the shaft 16, the mass distribution of the shaft 16 is varied vertically to vary the resonant frequency or critical speed of the pump. lf a greater degree of variation of resonant frequency is desired, a heavier weight 48 can be positioned on the shaft 16.

Thus, it can be seen that the operating speed of a cantilevered shaft pump can be varied to any desired r.p.m. and never approach a critical speed simply by repositioning or varying the mass of the weight 48. This in effect changes the mass distribution of the pump shaft i6, thereby changing the resonant frequency. In this manner, the pump performance is always consistent and eilicient, but with the pump being adapted to be driven at any elected speed.

The motor l2 and outlet pipe 22 can be secured to any desired type of support means :to suspend the shaft 16 and associated means for pumping action.

It should be realized that the weight 48 used in the pump shaft lo can be of any suitable type, and that usually a sleeve-like member is provided, which sleeve can be secured to the shaft i6 at any desired vertical position thereon to vary the resonant frequency of the cantilevered pump shaft. Such weight member, if an actual sleeve is used, can be associated with the shaft prior to assembly of the pump impeller thereon, or the weight member can be split axially to be engaged with the pump shaft by a clamp action and usually have some set screw member in the weight means engaging the periphery of the pump shaft to xedly secure the weight means thereto. It will be seen that preferably the weight means used is at least substantially balanced circumferentially around the periphery of the shaft. The position of the weight is readily adjustable when the operating speed range of the pump shaft is changed so that, if any undesirable vibrations due `to critical speed are set up in the pump shaft, the natural frequency of the pump shaft can be altered readily by changing the position of the weight on the shaft, by removing the weight from the shaft, or by adding additional weights to the shaft, as desired.

The electric motor 12 may be either of fixed, or variable speed, as desired. Likewise the motor may be directly coupled to the shaft 16, or be coupled thereto by a belt drive, or the like.

It will be recognized that the invention is an improvement applicable to each, or any of the pumps which I have previously patented, as well as to any similar type of pump operating at or near resonant frequency. With my invention, it is possible to operate a cantilevered pump at variable speeds and still keep the resonant frequency lof the pumps sufliciently removed from its critical speed range so that the operating characteristics of the pump will not be affected.

While in accordance with the patent statutes one best known embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby but that the inventive scope is defined in the appended claims.

What I claim is:

1. In combination with a vertically cantilevered rotatably mounted pump balanced shaft, a weight means, and removable means securing said weight means to the pump shaft at a selected but adjustable position along the axis of said pump shaft, whereby changing the position of said weight means along the axis of said pump shaft changes the inherent resonant frequency of the shaft.

2. In combination, a load carrying rotatably mounted, vertically cantilevered type shaft, said balanced shaft being of essentially the same diameter throughout its length, a tubular weight means on said shaft, and screw means securing said weight means removably and adjustably to the shaft at any portion thereof, said Weight circumferentially surrounding and being at least substantially equally circumferentially distributed on said shaft, said weight changing the mass distribution of the shaft when moved axially thereof.

3. In a vertically cantilevered pump unit, the combination of a motor, a rotatable balanced shaft xedly secured to the motor and extending vertically downwardly therefrom, an impeller iixedly secured to the shaft at the downward end thereof, a pump assembly surrounding the impeller, at least one discharge pipe attached to the pump assembly and extending ventically upwardly therefrom, a discharge chamber containing the upper end of the discharge pipe, said discharge chamber and discharge pipe supporting the pump assembly, a weight means, and means securing said weight means to the pump shaft at any one of a plurality of positions along the axis of said pump shaft, whereby changing the position of said weight along the axis of said pump shaft changes the inherent resonant frequency of the shaft.

4. ln a vertically cantilevered pump unit, the combination of an electric motor, a rotatable balanced shaft operably secured to the motor and extending vertically downwardly, bearing means engaging the shaft adjacent the upper end thereof, an impeller iixedly secured to the shaft at the downward end thereof, a pump assembly surrounding the impeller, a plurality of discharge pipes attached to the pump assembly and extending vertically upwardly therefrom, a discharge chamber which operatively connects to the upper ends of the discharge pipes, said discharge chamber and discharge pipes supporting the pump assembly, said shaft having essentially the same diameter in that portion of its length between the top of the pump assembly and the bottom of the discharge chamber, a weight means, and means to removably secure said weight means at any position on that portion of the shaft between the top of the pump assembly and the bottom of the discharge chamber, whereby changing the position of said weight along said shaft portion changes the inherent resonant frequency of the shaft.

5. In a vertically cantilevered pump unit, the combination of a motor, a rotatable balanced shaft of uniform diameter operatively secured to and driven by the motor and extending vertically downwardly therefrom, means securing said motor in a fixed position, an impeller tixedly secured to the shaft alt the lower end thereof, a pump casing surrounding the impeller, a plurality of discharge pipes attached to the pump casing and extending vertically upwardly therefrom, a discharge chamber containing the upper ends of the discharge pipes, said discharge chamber and discharge pipes supporting the pump casing, a weight means, and means securing said weight means to the pump shaft at one position along the axis of said pump shaft, whereby changing the position of said weight along the axis of said pump shaft changes the inherent resonant frequency of the shaft.

6. ln combination, a load carrying rotatably mounted, vertically cantilevered type shaft, a longitudinally split tubular weight means on said shaft, means securing the longitudinally split sections of said weight means together, said split sections being of substantially equal size and weight, and screw means engaging and securing said weight means removably to the shaft at any portion thereof, said weight means circumferentially surrounding and being at least substantially equally circumferentially distributed on said shaft, said weight changing the mass distribution of the shaft when moved axially thereof.

7. In combination, a load carrying rotatably mounted, vertically suspended, cantilevered type balanced shaft, said shaft being of essentially the same diameter throughout its length, a dianietrically split tubular weight means comprising -wo equal size and at least substanially equal weight sections on said shaft, screw means securing said Weight means together, and screw means removably securing said weight means to the shaft at any portion thereof, said Weight means circumferentially surrounding and being at least substantially equally circumferenrialiy distributed on said shaft, smd Weight means changing the mass distouion of the shaft when moved axially there- Referenees Cited by he Examiner UNITED STATES PATENTS Richardson 74573 Haentjens et al 103-102 Haentjens et al 10S-102 Haenjens 103--111 Langsetmo` 74-573 of whereby the critical frequency of the shaft can be 1Q LAURENCE V EFNER Primary Examiner' ROBERT M. WALKER, Examiner.

varied for different operating speeds. 

3. IN A VERTICALLY CANTILEVERED PUMP UNIT, THE COMBINATION OF A MOTOR, A ROTATABLE BALANCED SHAFT FIXEDLY SECURED TO THE MOTOR AND EXTENDING VERTICALLY DOWNWARDLY THEREFROM, AN IMPELLER FIXEDLY SECURED TO THE SHAFT AT THE DOWNWARD END THEREOF, A PUMP ASSEMBLY SURROUNDING THE IMPELLER, AT LEAST ONE DISCHARGE PIPE ATTACHED TO THE PUMP ASSEMBLY AND EXTENDING VERTICALLY UPWARDLY THEREFROM, A DISCHARGE CHAMBER CONTAINING THE UPPER END OF THE DISCHARGE PIPE, SAID DISCHARGE CHAMBER AND DISCHARGE PIPE SUPPORTING THE PUMP ASSEMBLY, A WEIGHT MEANS, AND MEANS SECURING SAID WEIGHT MEANS TO THE PUMP SHAFT AT ANY ONE OF A PLURALITY OF POSITIONS ALONG THE AXIS OF SAID PUMP SHAFT, WHEREBY CHANGING THE POSITION OF SAID WEIGHT ALONG THE AXIS OF SAID PUMP SHAFT CHANGES THE INHERENT RESONANT FREQUENCY OF THE SHAFT. 